Discrimination of host sex by a haematophagous ectoparasite

Sex biases in parasite infestation are known for various host–parasite systems. In most cases, males of higher vertebrates are infested by more parasites than females. The mechanisms behind male-biased infestation may include not only more opportunities for males to encounter parasites and/or better performance of a parasite in male hosts but also active selection of these hosts by a parasite. To test this hypothesis, we studied behavioural responses of the flea Xenopsylla ramesis to males and females of its common rodent host Meriones crassus in Y-maze trials. We asked whether an individual flea is able to discriminate between male and female hosts and choose a male host, and whether previous experience of the fleas (never fed, fed once on a male host, fed once on a female host) affects the choice. Among 385 fleas, 62% made a choice. In general, proportions of female fleas making or not making a choice of a rodent did not differ significantly, whereas the majority of male fleas chose a rodent. Latency of rodent choice was similar between male and female fleas, but was strongly affected by experience: fleas that previously fed on a male rodent or were never fed made their choices significantly faster than fleas previously fed on a female rodent. Among fleas that made a choice, selection of a male versus a female rodent depended on flea sex only. Male fleas chose randomly between a male and a female rodent, whereas female fleas chose a male rodent significantly more often than a female rodent. Our results suggest that male-biased flea infestation may involve active choices of male hosts by fleas.